This application claims the priority benefit of Taiwan application serial no. 89116722, filed Aug. 18, 2000.
1. Field of the Invention
The present invention relates to a method of forming a polysilicon layer. More particularly, the present invention relates to a method that effectively converts an amorphous silicon layer into a polysilicon layer by increasing the intensity of a laser beam using the super-resolution near-field structure.
2. Description of the Related Art
In recent years, polysilicon TFTs (p-Si TFTs) that have a high electron mobility are employed for forming the switching devices of high-density pixels of active matrix driven LCDs because amorphous silicon thin film (a-Si TFTs) transistors have a low electron mobility. In addition to the advantage of having the high electron mobility, the p-Si TFTs can also be used as a periphery driving circuit of a display. Thus, the p-Si TFTs are the subject of a great deal of attention and the technology for fabricating a high-quality polysilicon has became one of the major technology for manufacturing p-Si TFT transistor displays.
FIG. 1 is a schematic diagram illustrating a conventional method of forming a polysilicon layer using an excimer-laser annealing.
First, as shown in FIG. 1, an excimer-laser beam 18 having a vertical width of 5 nm and a horizontal width of 10 nm is used to irradiate a substrate 10. The excimer laser beam 18 moves along a direction 20. An amorphous silicon layer 12 on the substrate 10 is entirely irradiated by the laser beam 18 as it moves along the direction 20. Since the excimer-laser beam 18 is a pulsed excimer laser, the amorphous silicon layer 12 must be repeatedly irradiated during the annealing process to assure that the entire amorphous silicon layer 12 is sufficiently irradiated.
In the above-mentioned laser annealing process, the amorphous silicon layer 12 is subjected to a pulsed laser beam. Pulses of the excimer-laser beam 18 are used to irradiate the amorphous silicon layer 12. By repeating irradiation on the amorphous layer 12, the amorphous layer 12 is melted and then converts to a polysilicon layer. However, defects are created along an edge 16 of the irradiated regions of the polysilicon layer 14 after being irradiated by the excimer-laser beam 18. In addition, the energy applied on the edge 16 is different from the energy applied on other regions. Thus, there is a great difference between the polysilicon layer formed along edge 16 and the polysilicon layer formed on the other regions. In addition, because energy is received in different amount, the crystallization quality of the polysilicon formed along the edge 16 is poor. Therefore, during the repeating excimer laser irradiation, the region to be irradiated usually overlaps with a portion of a previously irradiated region in order to assure the quality of the polysilicon on the edge region 16.
The current excimer laser has an output power of about 100 watts. Thus, during the laser annealing process, the amorphous silicon layer 12 must be repeatedly irradiated by the laser beam 18 to assure the quality of the polysilicon along the edge 16. When the size of the array substrate 10 increases as the requirement of large liquid crystal displaying apparatus increases, such excimer-laser annealing process not only consumes a large amount of energy but is also very time-consuming. Consequently, the fabrication cost significantly increases.
The invention provides a method of forming a polysilicon layer. A light shield layer having a super-resolution near-field structure is arranged on an amorphous silicon layer. The super-resolution near-field structure includes a first dielectric layer, a second dielectric layer, and an active layer between the first dielectric layer and the second dielectric layer. The light shield layer is irradiated by a laser beam having a first intensity to generate a transmitted laser beam having a second intensity. The second intensity is greater than the first intensity. An annealing process is performed to irradiate the amorphous silicon layer with the transmitted laser beam having a second intensity thereby converting the amorphous silicon layer into a polysilicon layer.
In the present invention, the super-resolution near-field structure includes the active layer having a thickness of about 15 nm, the first dielectric layer having a thickness of about 20 nm, and the second dielectric layer having a thickness of about 170 nm. A material for the first dielectric layer and the second dielectric layer includes silicon nitride (SiNx), gallium nitride (GaNx), aluminum nitride (AlNx), and titanium nitride (TiNx). In addition, a material for the active layer includes gallium (Ga), germanium (Ge), arsenic (As), selenium (Se), indium (In), tin (Sn), antimony (Sb), tellurim (Te), and silver (Ag).
The invention uses a super-resolution near-field structure to increase the intensity of the excimer-laser beam. Thus, the present invention has no disadvantage of repeating irradiation as disclosed in the conventional method.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.